Diffusion and gas behaviourIB MYP Chemistry: Mind map

Exam questions on Diffusion and gas behaviour

1. A teacher in Johannesburg places cotton wool soaked in concentrated ammonia solution at one end of a long, horizontal glass tube, and cotton wool soaked in concentrated hydrochloric acid at the other end. Both ends are sealed with bungs. After a few minutes a ring of white solid (ammonium chloride) forms inside the tube, closer to the hydrochloric acid end than to the ammonia end.
   A particle of ammonia has a relative mass of 17 and a particle of hydrogen chloride has a relative mass of 36.5. Explain why the white ring forms closer to the hydrochloric acid end.2 marks
2. A student in Oslo uses a microscope to look at smoke in a small glass cell lit from the side. The student sees tiny bright specks of smoke ash that jiggle about in random, jerky paths, constantly changing direction. The specks never stop moving, even though the air in the cell is perfectly still.
   Explain why the smoke specks move in random directions rather than in a straight line.2 marks
3. A student in Wellington investigates how temperature affects diffusion in a liquid. She drops one small crystal of potassium manganate(VII), which is purple, into each of three beakers containing 200 cm³ of water at different temperatures, without stirring. She uses a stopwatch to time how long it takes for the purple colour to spread evenly through the water, judged by eye. She wears safety glasses throughout.
   State a testable hypothesis for this investigation, with a scientific reason.3 marks